A hot-melt adhesive is a solvent-free adhesive and has a characteristic that instant bonding and high-speed bonding can be achieved since adhesiveness is exhibited after the adhesive is melted by heating and coated onto an adherend, followed by cooling to solidify the adhesive, and therefore has been used in a wide range of fields. Not only adherends to be bonded with such a hot-melt adhesive but also the conditions of use thereof are various. At present, various hot-melt adhesives for use in various applications have been developed and supplied to the market. Also for the conditions of use, various operating temperatures ranging from low temperatures to high temperatures are considered.
In general, a creep phenomenon occurs such that when a given stress is applied to a bonded part for a long period of time, even if the stress is not higher than the breaking strength of an adhesive, elongation occurs to cause breakage, and this phenomenon prominently occurs under high temperatures. In recent years, a hot-melt adhesive having excellent heat resistance, particularly excellent heat creep resistance has been demanded.
PTL 1 discloses a hot-melt adhesive containing an ethylene-based copolymer as a base polymer and also containing a tackifier resin and a wax. This adhesive has high adhesive strength at low temperatures, but its heat resistance, particularly heat creep resistance is poor as an adhesive.
PTL 2 discloses that in order to improve the heat resistance of a hot-melt adhesive, a specific polymer (a functionalized metallocene polymer) is used as a base polymer. However, the hot-melt adhesive described in PTL 2 does not fully satisfy the heat resistance requested by users.